The present invention relates to a semiconductor device and a manufacturing method thereof, and particularly to a solid-state image sensing element having a so-called backside-reflection light receiving element and a manufacturing method thereof.
A solid-state image sensing element is a semiconductor device in which, over a front surface of a semiconductor substrate, electrodes, interconnects, and a light receiving element such as a photodiode are formed. The solid-state image sensing element typically has a so-called frontside-illuminated structure in which the light receiving element is illuminated with light for photoelectric conversion which is applied thereto from above (the front side thereof).
However, since the frontside-illuminated light receiving element is illuminated with the light applied thereto from above the metal interconnects formed above the light receiving element, a problem arises in that a part of the light is reflected by the metal interconnects or the like and the light does not efficiently reach the light receiving element. To solve the problem, a solid-state image sensing element having a so-called backside-illuminated structure has been developed in which a light receiving element is illuminated with light for photoelectric conversion which is applied thereto from below (from the back side thereof). A solid-state image sensing element having a backside-illuminated structure is described in, e.g., Patent Document 1.
Patent Document 1 shows the solid-state image sensing element as a CMOS (Complementary Metal Oxide Semiconductor) image sensor particularly having a global electronic shutter function. In the solid-state image sensing element as the CMOS image sensor having the global electronic shutter function, light simultaneously supplied to individual light receiving elements is simultaneously converted to signal charges by photoelectric conversion and stored in capacitor elements coupled to the individual light receiving elements. Since the charges including the signals simultaneous with each other are stored in the capacitor elements, when the signal charges are successively read, distortion of an image resulting from a time lag can be inhibited.
In Patent Document 1, a first substrate formed with the light receiving elements and a second substrate formed with the capacitor elements are joined together at a junction surface so that the capacitor elements are placed so as to overlap the light receiving elements (pixels including the light receiving elements) in planar view. Accordingly, by receiving light from the light receiving element side, it is possible to implement the backside illumination described above and also inhibit a reduction in the area of the region where the light receiving elements are placed due to the capacitor elements occupying the surface area of the substrate. This allows a high-performance solid-state image sensing element to be formed in which the light receiving elements occupy a large area part of the surface area of the substrate.
Besides, in a solid-state image sensing element having, e.g., so-called wide dynamic range performance also, signal charges are stored in capacitor elements coupled to individual light receiving elements. Specifically, the solid-state image sensing element is provided with the capacitor elements having the function of temporarily storing and keeping therein signal charges such as electrons stored in the light receiving elements or electrons generated in excess of the saturation charge capacity of each of the light receiving elements in the light receiving element and a floating diffusion layer capacitor associated therewith.
If the light supplied to the light receiving elements illuminates the capacitor elements storing therein the signal charges, the signal charges stored in the capacitor elements may leak out of the capacitor elements. For example, if the signal charges stored by the global electronic shutter function leak out of the capacitor elements prior to a read operation, correct image signals cannot be read during the read operation. Therefore, a light blocking film for inhibiting the foregoing illumination with light is preferably placed for the capacitor elements.
A solid-state image sensing element having a configuration in which the incidence of light on capacitor elements is inhibited by providing a light blocking film above capacitor elements is disclosed in, e.g., Patent Document 2. Patent Document 2 discloses the capacitor elements storing therein signal charges for outputting dark currents from effective pixels in a state where light is prevented from being incident on the effective pixels.
Thus, a solid-state image sensing element as a CMOS image sensor is mostly provided with capacitor elements for temporarily storing signal charges supplied from light receiving elements.